Piston ring



. 26, 1937. w. WUER'IFEL PISTON RING originalii l ed Sept. 9, 1930 2Sheets-Shae}. 2

INVENTOR WILLIAM WUERFEL ATTORN EY I Reissues! Jan. 26, 1937 UNITED.STATES PATENT OFFICE I l'ls'roN RING William Wueriel. Philadelphia.rs., a-ignor to", Wllhenlng llanniactnring compl m We! phiglaaeorporationoillelaware 4 Original No. 1313392, dated July '1. 1031,serial No. 480,786, September 9, 1930. Application ior reissue July a,1931. Serial No. 549,530

1': cum. sea-4s):

My invention relates to certain new and useiul piston ring constructionadapted particularly ior controlling theoil within the cylinders 01internal combustion engines and the like, and it relates ,5 moreparticularly to a piston ring construction wherein a plurality oi split,annular rin s are operativsly disposed within piston, and are sorelated-to each other and to the ring groove, as to aiiord eiiectivemeans for preventing excess oil irom passing the piston into thecombustion chamber; 'at the same time permitting a propenand sumcientlubrication oi the cylinder wall and minimizing the frictionalresistance and wear due to the rings, and which will also'tend toeil'ect a pressure proof seal betweu pistonandcylinder. t v

This application is a continuation, in part, oi my earlier flledcopending applications, Serial Number 425,638 and Serial Number 456,350.

It is an object oi my invention to provide an eilective oil control ringwhich will be efllcient in the conservation oi the oili within the crankcase oi the engine, which will nevertheless permit sumcient lubrication,and which at the; same 2 time will aiiotd a minimum irictionalresistance to the reciprocation oi the piston and a minimum wear andheating eiiect. With the above and other objects in view, whi

will appear more iully irom the iollowing de- 3o tailed description, myinvention consists oi a 40 ring and-at least one'oi which is positionedon the lowermost part oi the corresponding ring, and recesses or notchesin. and extending,trans-' versely across, one or moreoithe abuttingc'ontiguous side walls or iaces oi said plurality'oi s rims, and meansoperativelv interposed between the innercylindrical wall or bottom" oiring groove. and theinner peripheral suriaces of each oi said rings, iorexerting auniiorm outward 11-,

dialpre'asure upon each-oisaid rihgsi-andbne 0 01 presenting a planeside-seatingsurface in tive; juxtaposition ,tothe respective sideewalloi thering-receiving groove having an eiiective area substantiallydiilerent irom the eiiective area oi the side-seating iuriaoe presented55 bytheotherrlng in iustapoeitionto the other aring groove oi'the.

each oi, Figures 1 and 4 to 'l inclusive,

side-wall oi the: ring-receiving groove, and the, lower and upper, outerperipheral edges of the successive cylinder-contact or cylinder-sealingsuriac'es presenting substantially diflerent angles for producingsubstantially diiierent "oil-scrap- 5 ing'" eil'ects during the twoopposed strokes oi reciprocatory movements'oi the piston. My inventioniurther consists 0! other ieatures 'oi construction which will appearmore fully irom theiollowing detailed description oi my invention andthe accompanying drawings.

For the purpose oi illustrating my invention. I have shown in theaccompanying drawings iorms thereoi which are at present preierred byme. 'sincethe same have been iound in practice 5 to give satisiactoryandreliable results, although it is to be understood thatthe variousinstrumentalitiesoi which my invention consists can u be variouslyarranged andorganiaed and that my inventionis not limited to theprecisear- 20 rangement and organization oi the instrumentalities as hereinshown and described.

Figure 1 represents a side elevational view. partly in section (on line1-4 oi Figure 2), with the fragmentary portion oi the cylinderand-piston.

Figure 2 represents a section taken general on lined-I oi Figure l.Figure 3 represents an elevation oi the radial expander spring. a

Figures-4 to '7 inclusive re nt side-elem 1 ticnal views, similar toFigure 1, illustrating modified embodimmts oi my invention.

In carrying out my invention, I may utilize any conventional piston lladapted ior operation '35 within any conventionalcylinder Ii and anysuitable number oi ring-receiving groovbs: said piston ring it andylinder ii being illustrated inthe drawings in a iragmentary manner.novel piston ring construction includes an 40 upper and a lower splitannular designated by numerals i2 and it. W vely. the aggregate overailwidth oi which nds generally with the width oi thefrl g groove ilz-therebeing however a llilht lateral '01 5 axial clearance betweenitlie ringsand the side wallsoi theringgrooveindicatedat II. The successiveindividual and separate annular rings are preferably, though notnecessarily. oi equal. overall width and are chamiered or otherwise setoil or rabbeted' upper and outer circumierential edges, a's-will beseenin Th'eupperand lower chamiera u e u re? sw a. c and'D- oiuieu perchamas I fer II andthelower rabbetinggroove ll, (Figures 1 and 4) formcorresponding upper and lower annular oil-collecting chambers. Thesesuccessive and spaced non-communicating annular oilcollecting chambers,formed by the'upper and lower chamfers ll and II, as in the case oftheforms of my invention shown in.l"igures 5, B and '7, or the upperchamfer l6 and lower rabbeting groove It in the modiflcations of myintions is and of the rings l2 and II, to about one-half of the width ofthe corresponding It will thus be seen that below each of thecircumferential annular oil chambers is a comparatively. narrow annularcylindrical contact surface I! and 20, respectively, adapted forcontactwith the cylinder wall ll.

It will be observed that the lower circumfer-- ential corners or edges2i and 2-2 respectively, of

each of the ring members I2 and II, are formed of two surfaces at aright angle to eachother.

i. e.; the lower side wall of the corresponding ring member and thecylindrical contact portions l9 and 20 respectively. The upper outercircumv in advance of the lower right angular edge 22;

ferential corners or edges 28' and 24 respectively. are, on the otherhand, both formed of two surfaces meeting at an obtuse angle to eachother as in the modifications illustrated in Figures 5, 6 and 7;or atlea'st the upper edges 23 are formed at an obtuse angle. while the loweredge 24 is formed at a right angle; as in the, modificationsshowninFiguresland i i r The eil'ect of the pair of successive lowerright angular edges 2| and 22', and the pairof successive upper edges,oneor both of which are at an obtuse angle, is to provide a greater oilscraping action on-the down-stroke of the piston ,and a lesser oilscraping action on the up-stroke of the piston;--with a resultanttendency to cause a general removal .of oil from the cylinder wall inthe direction of the crank case and with the further resultant tendency;on the downstroke, to gather a greater part of the affected oil togather a lesser part of the aflected oil -in ad chamber l1 or l8,'and togather a still lesser I or II and I8, asthe casemaybe.

vance. of the lower edge 2-1, into the annular part of the affected oilinto the upper annular chamber It. If the particular ring groove is notthe uppermost groove of the piston, then a certain amount of oil isscraped into the upper; annular chamber It by the'ring aboveit in thethis construction and relationship of constituent elements, is to effectan eflicient lubrication of 7 cylinder walls by reason of the releaseof'some of the entrapped oil in the chambers ll and II In one or both ofthe abutting or con side walls or faces of the'rlngs l2 and It, a series(any suitable number) of relatively shallow recesses 2i of'generallyuniformdepth, are provided. extending generally transversely orradiallyacross the. inner side or face of the ring: .withtheirouterendstermlnatingintheeormerrabbeting or chamfer of thecorresponding ring or in the cylindrical cylinder-contact orcylindersealingsurfaceofthering andwiththeirinner ends terminating onthe inner circumference thering. Throughthese'reoeles 2laswellaspossibly through the slight clearance indicated at some innerperipheries of the rings J2 and "and -"bottom 21, respectively. of thering groove l4.

ll,whichclearancemayshiftfromthebottomof the groove to the topof thegroove or divide therebe'tween (or which may also be between'the tworings) a portion of the oil is transmitted inaninwardradialdirectionintotheringgrowe. it behind the rings i2 and II,from whence the excessoilisdrainedbackintothecrankcase through the drainhole 2| in the wall of the piston. It is this portion of the .oil whichotherwise enters the combustion chamber and. results in what'isgenerally referred to as "oil-pimping.

The other portion of the oil adhering to the cylinder wall is scrapeddown and into the crankcase by the'low'ermost edge 22 of the-ring ll.

vThe recesses 25 are preferablyofuniform depth and made with outwardlydivergent side walls or edges as indicated in Figure 2. ,The outwardlydivergent side walls or edges of-the recesses 25 are convexly curved andpreferably have a common center at-a point outside of the radiallyoutermost boundary of the ring.

Intermediate the inner circumferential walls,

of the rings l2 and i8, and the inner wall or bot tom 21 of the ringgroove is, aradially acting gat ribbon expander spring 28 is provided.of the general type disclosed in my Patent Number 1,707,035, preferablyhaving a sinuous'corrugated formation giving rise to opposite andstaggered contact portions adapted for contacting with the e Theexpander spring 2. is preferably narrowed at the inner contact points 20thereof, and slotted longitudinally by means of' the slots 20 at theouter contact portions ll thereof. By reason of the'slottlng of theouter contact portions 8|, two independently flexible contact points 32and II are provided for contacting engagement with the two separaterings l2 and I2 respectively. This independent flexibility and resultantequalimtion is further augmented by the narrowing at the inner points ofcontact 29. This narrowing also reduces the impedance to the passage ofthe. oil. Due to the limited independent flexibility of the upper andlower contact'points 32 and 33. the rings i2 and II are urged outwardlyby the expander spring 28 -pvith an equalised or compensated outwardradial pressure. Thus any diiference in over-all radial width of therings l2 and I; or any variation inthe diameter of the cylinder in anaxial direction, will not cause a firmer contact between the cylinderwall and one of the rings than between the cylinder wall and the otherof the two rings. bees-use any such slight diiferencelis compensated foror equalised by the of the upper and lower edges o'f'the two rings maybe maintained, free of any variation which might otherwise be occasionedby diiferenee' in.

contact pressure between the rings and wall fiat. ribbon, radialexpander spring 2' e xpands the rings l2 andv Itindependently of anyotherexpandingmeanassforinstancatension in the rlnfl. or said radialexpander spring augmentstheoutwardtensionsetintothebody of the rings byany suitable means. as for in stance theheat-shaping or heat-tensionin'gdisjclosed ifithe PedrichlsKolb Patent No 1,284,439. Thus thesplitannular rings l2and I! may be setto' give an outward tension,'byheat-shaping thenuor otherwise, and a suitably tensioned flat.

ribbon. radial expander spring 2| is operatively interposed betweentheinner peripheries of the "ls throughout the entire periphery thereof.and so ring members It and-it and the inner wall of the ring-receivi sgroove, to center such rings with respect to the piston, so that thevarious oil controlling functions of the rings and their constituentelements. are made more uniform jthat the collapse of the rings isprevented. The eflective width of the flat. ribbon, expander spring is'made less than the'width of thering-receivinggroove,soastopermitfllefreepassageofoilfromtheradialoilpassagewaysofthering,'

through the oil chamber formed between the inner peripheries of ringmembers and the inner wall of the ring-receivinggroove. into the oildraining apertures 20.

The clearance between the aggregate over-all width the two rings it andlland the width of the groove II is preiflerably made aboutfivethousandths cfaninch (more or less). This clearance. when used inconjunction-with the motor oils of a viscosity within the viscosityrange commonly employed for internal combustion engines, will produce asuiiicient radial passageway I between the outer and inner circumferenceof the ringsandwillatthesametimemaintainaiilm or layer of oil, by reasonof the viscosity. cohesion and adhesion of'the oiL-and possibly also byan eifect similar to, if not in fact of, the capillary action due to thesurface tension or the oil in the comparatively narrow clearance.Because of the greater side-contact surface or side-seating be- .tweenthe lower side face of the lower ring II a and the adjacent side-wall ofthe ring-receiving edge I! of the lower ring it toconvey a portion'of-the oil from the cylinder wall into the rear groove. than betweenthe upper side-face or sidesesting surface of the upper ring if andtheadiacentside-wall of the ring-receiving groove, the clearance willtend to form more between the lower ring and the adjacent lower sidewall of the ring groove, as indicated particularly at II in Figure l.This'coacts with the lowerscraping of the ring groove it to the drainholes ll, "lhe pil aifected bythe edges Ii and I4 is conveyedtotherearoftheoiigroovebytherecessesfl. The

clearance II is greater than that to "at" the width of the ringgroove:-the normal "flt" clearance being about one-thousandth or one andone-half thousandth. while the clearance forming a part of my presentinvention is approximately five-thousandths of an inch (more or less)sumcient to maintainthe layer of oil. which will not only .aiford adraining means but whichwiii also ail'ord a cushion for the rings.

Theresult of thisnovelconstructicmaspcinted out hereinabove, is a highlyemcient oil controlling or oil conserving means; which will at the sametime maintain a suihcient and proper lubrication of the cylinder walland reduceto a minimum the frictional resistance to the action of therings.

I am aware that the-invention maybe embodied in other specific iormswithout considered in all respects as illustrativeand not restrictive.rsferencebeing had to theapp'endedclaim'sratherthantotheforegcingdescriptionto indicate thelcopeoftheinvention.

Ham thus'described my invention. what I herebyclaim as newanddes'lretosec'ureby Letters Patent, is:

1.1hecombinationwithacflindenofaysstnn adapted to an annular and wearincidental departing from the spirit or essential attributes thereof.and I therefore desire .the present embodiment to be are integral witheach other, and or an axially divided, multi-piece, split, annularmetallic piston-ring having anouter annular oil-collector groove in'theouter cylindrical surface thereof, a plurality of peripherallydistributed generally radialoilp extending fromsaid outer annularoil-lltor groove through the pistonring, into an oil chamber formedbetween the inner peripheral surface of the piston-ring and the innerwall of the ring-receiving groove; the

.dimensicns of said radial passageways in a direction generallyconcentrically with the periphery of the ring being greater than theirdimensions in a direction generally parallel to the axis of the ring.and lateral or axial clearance between piston ring and ring-receivinggroove in excess of the normal clearance required to fit the pistonringinto said groove, suiiicient to permit the formation and maintenance ofa layer of oil in said lateral clearance between piston-ring andring-receiving 'groove;e ach of said ring members having an outerside-seating surface for "side-seating engagement with the respectivesidewalls of the ring-receiving groove, and the alientive area of one ofsaid two side-seating surfaces being substantially less than theeii'ectlve area of the other of said side-seating surfaces.

2. The combination with a cylinder and able-- ton adapted to'trav'eltherein, the latter having an annular ring-receiving groove therein, thede-- lining walls of which are integral with each other, of an axiallydivided two-piece. split, annular cast-iron piston-ring having an outerannular oil-collector groove in the outer cylindrical surface thereof,divided between the two annular ring members comprising saidpiston-ring, a series of peripherally spaced and generally radial oilpassageways extending from said outer annular oil-collector groovethrough the piston-ring, into an oil chamber formed between the innerperipheral surface of the piston-ring and the bottom ofthe'ring-receiving groove, the dimensions of said radial passageways ina direction concentric of the ring, and lateral or axial clearancebetween piston-ring and ring-receiving groove in excess -of the normalclearance required to lit the pistonring into thegroove,suillcienttopermit the formation and maintenance of a layer of oil. insaid lateral clearance between piston-ring and ring- 1 receivinggroove;--esch of said ring members having an outer side-seating surfacefor sideseating engagement with the respective side-walls of thering-receiving groove; and the eifective area of one of said twoside-seating surfaces benular piston-ring. having'a plurality of generalI! radial oil passageways peripherally distributed with the periphery ofthe ringbeing greater than their dimensions in a direction parallel tothe axis a m fm m u w .v .m u, 1 47 H. a m m W... mZ m a. I... wim urmmpmm mmwmwmm W. WWWM WW WWWW WW WWWMWMWWW MWWWWWWWWWWW WWWWWWWMWWWWWWWWWWWWWWWW WWWWWWW W WWW mm a, W m MW m ..W W; W WmWMWWWWWWWQWMW WW W W. W, WW WWWW W a W m W W WW W W W MW..W WW W WW W Wm W WW WWW. W W W M W WW MW W W W W WWWWW WW WW M MW WWM ZWW M WW ram WWZ W. WW.WWW W W m WW W WW W WW. W W rm WWWWWWMWW WW WWW W M W WWW W.WWW WW W W WWWW W WWW W WW WWWW WWWWW W W W WW WW WWWWWW WWWWW WVWWWQMWWW .WWWWMWNWWWW .WWWWWWWM ..WWMWWWM WWWW .MMWWWWWMWWWWWWWMMWWWMM wWWW. W WWWWWWW WWWWWWWW WWWW W WWWWWWWW WW WWWWW W W W WWWWWW W WWWWWWWW WW W WW WW WWW WWW WWW WWWW W WWWWWW W WW W WW W ..MWWWWW MWWWMWWWWWMMMWWM Fm WWWWMWWWWWMMWMWWWMW WW WWMW WWW W W: w W :MWWFMM WW W WWWWMW WW Z W w mm a m W m M.. u mm v WWWW WWWWW W WWWWWW W W W WWWW WWWWW W WW WW WW W r W ..W., W w W W W W. W WW m. n W m W 4 m Mm mMm mmmmwmm m W m m m m WWW m mmm/ m MM um a W a a v, m m n mmm mm m mmmm nm wmmnm WW W WW W M WW M W WWWW W WW W W WW WWWWWWWW WW WW WWWWWWWW WWWMWWWWW WWWWWWWWW WWWWWWWW WWWMWWW WWWWWWWW ,W WW

into said groove, sufiicient to permit the formation and maintenance ofa layer of oil in said lateral clearance between piston-ring andringreceiving groove, and a single expander spring outer side-seatingsurface for side-seating engagement with the respective side-walls ofthe ring-receiving groove, and the elective area of theupper of said twoside-seating surfaces beingsubstantially less than the elective area ofthe other of said side-seating surfaces.

8. Thecombination with a cylinder and a p ton adapted to travel therein,the latter having an annular ring-receiving groove therein, the

' defining walls of which are integral with each other, of an axiallydivided two-piece, split, an-

nular cast-iron piston-ring having an outer annular oil-collector groovein the outer cylindrical surface thereof, divided between the two annular ring members comprising said piston-ring,

a series of peripherally spaced and generally ratheir outer ends openingin the outer peripheral dial oil passagewaysv extending from said outerannular oil-collector groove through, the pistonring, into an oilchamber formed between the inner peripheral surface of the piston-ringand the bottom of the ring-receiving groove, the dimensions of saidradial passageways in a direction concentric with the periphery of, thering being greater than their dimensions in a direction parallel to theaxis of the ring, lateral or axial clearance between piston-ring andrin'g-receivlng groove in excess of the normal clearance required to fitthe piston-ringinto the groove, suiiicient to permit the formation andmaintenance of a layer of-oil, in said lateral clearance betweenpiston-ring and ring-receiving groove, and T. single expander springintermediate the inner peripheral wall of the ring-receiving groove"nularplston and each of said ring members for exerting a'circumferentially distributed outward radial pressure upon each of saidring members;each of said ring members having an outer side-seatingsurface for side-seating engagement with the re,- spective side-walls ofthe ring-receivinggroove, and the elective area of one of said twosideseating surfaces being substantially less than the elective area ofthe other of said side-seating combination with a cylinder. of a pistonface tho cylin radialpassagewaysinacentricwiththepcrlpheryoftheringbeing & some normslclearance required toiit the piston-ring ring and ring-receiving groove, sumciently in excessof the normal clearance required to fit the piston ring into saidring-receiving groove, to permit the formation and maintenance of alayer of oil in said lateral clearance between pistonring andring-receiving groove; and a single expander spring intermediate theinner peripheral wall of the ring-receiving groove and each of said ringmembers for exerting a circumferentially distributed outward radialpressure upon each of said ring-members;each of said ring membershaving-an outer side-seating surface for sideseating engagement with therespective sidewalls of the ring-receiving groove, and the elective areaof the upper of said two side-seating surfaces being substantially lessthan the elective area of the other of said side-seating surfaces. v

' 10. The combination with a cylinder, of a piston adapted to traveltherein, the latter having an annular ring-receivinggroove therein. the

defining walls of which are integral with each other, and of an axiallydivided'two-piece, split annular metallic piston ring, having a seriesof peripherally spaced and generally radial oil passageways extendingthrough the ring with cylinder-contact surface of the piston ring andserving to scrape oil from the cylinder wall and to gather the said 011and to pass the same through the ring into an oil chamber form'ed bejtween the inner peripheral surface of the pistonring and the bottom ofthe ring-receiving groove, the dimensions of saidradial passageways in adirection concentric with the periphery of the ring being greaterthantheir dimensions in a direction parallel to the axis of the ring,lateral or axial clearancebetween piston ring and ring receiving groove,suiiiciently in excess of the normal clearance required to fitthepistonring into the groove, to permit the formation and maintenance of a layerof oil in said lateral clearance between piston-ring and ring-receivinggroove, and oil drainage means extending through the piston wall todrain the excess oil gathered by the piston-ring, and a single expanderspring intermediate'the inner peripheral I wall of the ring-receivinggroove and each of said ring members for exerting a circumferentialiydistributed outward radial pressure upon each of said ringmembers;eachof said ring members having an outer side-seating surfacefor sideseating engagement with the respective side-walls of thering-receiving groove, and the elective area of one of said twoside-seating surfaces being substantially less than the elective-area ofthe other of said side-seating surfaces.

11. The combination with a cylinder, of a piston adapted to traveltherein, having an annular ring-receiving groove, the defining walls ofwhich are integral with each other, and of an axially dividedmulti-piece, split, annular metallic pistonering, each ring membercomprising said multi-piece annular cylindrical cylinder-contact surfaceportion, continuous and uninterrupted annularly, except for the veryslight interruption at the split, the axial width of said continuous andannulariy uninterrupted cylinder-contact surfaceportions being less thanthe over-all axial widths of said ring mem-- bers, respectively. sseries of peripherally spaced and generally radialoilpassagewa'ylextending through the-pistonring, having their outer ends intu-m'ediatessidcentinumisandannularly 1mleast in parts, so as to permitthe generally free passage of. oil from said radial oil passageways oroil-collector groove in the outer cylindrical' surface thereof, aplurality of peripherally distributed and generally radial oilpassageways extending from said outer oil-collector groove through thepiston-ring, to an oil chamber formed between the inner peripheralsurface of the plston-ring and the inner wall of the ring-receivinggroove and said passageways being bounded by the ring members; thedimensions of said generally radial oil passageways in a directiongenerally concentric with the periphery of the pistonrlng being greaterthan their dimensions in a direction generally parallelto the axis ofthe pistonring; each of said ring members having an outer receivinggroove; an axially divided, multi-piece,

side-seating surface for side-seating engagement with the respectiveside-walls of the ring-receiving groove, and the effective area of thesideseating surface of the ring member nearest to the head of the pistonbeing substantially less than the effective area of the side-seatingsurface of the other ring member.

16. In combination with a cylinder and a piston adapted to traveltherein "and having an annular ring-receiving groove, the defining wallsof which are integral with each other and having oil-drainage meansextending through the piston-wall, adapted to drain oil from theringsplit, annular metallic piston-ring having an outer oil-collectorgroove in the outer cylindrical surface thereof, apluraiity ofperipherally distributed and generally radial oil passageways extendingfrom said outer oil-collector groove through the piston-ring, to an oil'chamber formed between the inner peripheral surface of the piston-ringand the inner wall of the ringreoeiving groove and said passagewaysbeing bounded by the ring members; the dimensions of said generallyradial o'il passageways in a direction generally concentric with theperipheryof the piston-ring being greater than their dimensions inadirectlon generally parallel to the axis of the piston-ring; and thedepth of said radial oil passageways-at their outer ends, in a directionparallel to the axis of the piston-ring, being generally the sameastheir corresponding depth at their inner ends, and a ribbon-expanderspring operatively interposed between-the inner peripheral surfacesof-each of said ring members and the inner wall of the ring-receivinggroove and within the said oil chamber formed between said surfaces, toexert a circumferentially distributed outward radial pressure upon saidring members;

said ribbon expander spring having an effective cross-section less thanthe width of the ring-receiving groove at least in parts, so as topermit the generally free passage of oil from said radial oilpassageways of said piston-ring through said 011 chamber formed betweenthe inner peripheral surface of the piston-ring and the inner wall ofthe ring-receiving groove and into said oil drainage means extendingthrough the wall of the piston. V a w 17. In combination with a cylinderand a piston adapted to travel therein and having an annularring-receiving groove, the defining walls of a which are integral witheach other andhaving oil-drainage means extending through thepistonwall,adapted to drain oil from the ring-receiving groove; an axially divided,multi-piece, split, annular metallic piston-ring, the component membersof which are capable of independent expansion and contraction. saidpiston-ring having a plurality of circumferentially distributed oilpassageways extending from the outer periphery of-said piston ring tothe inner periphery thereof, to an oil chamber formedv between the innerperipheral surface of the piston-ring and the inner wall of thering-receiving groove; the dimensions of said oil passageways in adirection generally concentric with the periphery of the piston-ringbeing greater than their dimensions in a direction generally parallel tothe axis of the piston-ring; said oil passageways having side wallsextending generally at a right angle to the axis of the piston ring andhaving outwardly divergent end walls, and a ribbon expander springoperatively interposed between the inner peripheral surfaces of each ofsaid ring members and the inner wall of the ring-receiving groove andwithin said oll chamber formed between said surfaces, to exert acircumferentially distributed outward radial pressure upon each ofsaid'independently flexible ring members; said ribbon expander having aneflective cross-section less than a the width of the ring-receivinggroove at least in age means extending through the wall of the piston.

